What is genetic carrier screening?

Carrier screening is testing that's done to see whether you or your partner carry a genetic mutation that could cause a serious inherited disorder in your baby. Some of the more common disorders screened for include cystic fibrosis, sickle cell disease, thalassemia, and Tay-Sachs disease, but there are more than 100 others that can be tested for.

Many of these conditions are rare, but one large study found that 24 percent of the patients tested were carriers of at least one mutation. And the average risk of having a child with one of these diseases is higher than that of having a child with Down syndrome or a neural tube defect. What's more, these conditions will not be detected by prenatal tests like CVS and amniocentesis unless you have carrier screening first.

Here's how it works: These disorders are recessive, which means that a baby must inherit a defective gene from each parent to have the disease. If you're a carrier of a defective gene for a recessive disorder, that means you have one normal copy of the gene from one of your parents and one defective copy from the other. (Carriers don't usually have any symptoms of the disease.)

If both you and your partner are carriers of a disorder like cystic fibrosis, sickle cell disease, or Tay-Sachs disease, your child will have a 1 in 4 chance of inheriting one defective gene from each of you and being born with the disease.

How is genetic carrier screening done?

Ideally, you should have the option of being screened before you try to conceive. Your practitioner should offer it to you at your preconception visit. This way, if you find out that you and your partner are both carriers for a condition, you'll have a wider range of options. You can talk to a genetic counselor who will be able to tell you more about the condition and help you sort out your reproductive choices. (More about that below.)

Traditionally, couples have only been offered screening for one or two of the most common mutations if they are determined to be at risk for being a carrier. Risk factors include having a family member with the inherited disorder or who's a known carrier, or being part of an ethnic group at increased risk for the disease.

The problem with this approach is that many people don't belong to distinct ethnic categories. Many people are mixed race, adopted, or simply can't be sure what ethnicity their ancestors were. So there's no good way of determining who's at risk for being a carrier of any particular mutation.

Instead, you can choose to be screened for a wide range of disease mutations – more than 100 instead of just the one or two you may be "at risk" for. This approach is known as expanded carrier screening. If your caregiver doesn't offer you expanded screening, you can ask for it.

If you opt to be screened, you'll be asked to give a blood or saliva sample. If you're found to be a carrier, your partner will be screened as well. Or both partners may be screened at the same time to get the results faster.

You should be given the option of talking with a genetic counselor before the screening and after you get your results. This person can help you understand your results and your options for planning your family.

You might also consider consulting a medical geneticist, a doctor who is specially trained and board certified in genetics. The American College of Medical Genetics and Genomics offers an online tool for finding genetic services.

How much does genetic carrier screening cost?

The cost of carrier screening has declined dramatically in recent years, thanks to advances in technology. Since carrier screening is a recommended part of preconception and prenatal care, it's sometimes covered by insurance. On the other hand, some insurance companies consider the testing optional and don't cover it. Out-of-pocket costs vary, but they're typically not more than a few hundred dollars, even without insurance.

What are our options if we find out we're carriers?

If you find out before you're pregnant, you may decide to try artificial insemination with sperm from a donor who is not a carrier. Another option is to have in vitro fertilization, with special testing of the embryo before it's implanted. (This testing is known as preimplantation genetic diagnosis and many insurance companies are now covering it.) Some couples decide to adopt a child instead or not to have children at all.

Unfortunately, many women are not offered carrier screening until they're pregnant. If you're already pregnant and want carrier screening, it should be done as early as possible in your pregnancy. This will give you time to talk to a genetic counselor about the possibility that your baby has one of these disorders and figure out whether you want to have diagnostic testing like CVS or amniocentesis to find out.

It's important to understand that CVS and amniocentesis won't automatically tell you whether your child has this kind of genetic disorder. You have to have the carrier screening first so you know what mutation you and your partner have and can ask the testing center to look for it.

Early screening may have other advantages. For some diseases, knowing your baby is affected before birth makes it more likely that your child can be helped by early treatment. It allows you to line up the right medical specialists, who can be on hand to start treating your child after delivery.

Below is more information on some of the more common genetic conditions that carrier screening tests for.

Cystic fibrosis screening

Cystic fibrosis (CF) is a life-threatening genetic disease. People with CF are prone to breathing difficulties (including lung infections and severe lung damage), digestive problems, and other complications.

People at high risk include Caucasians and people who have a relative who has CF or who is known to be a carrier. One in 29 Caucasians carries an abnormal cystic fibrosis gene, compared to 1 in 46 Hispanic Americans, 1 in 61 African Americans, and 1 in 90 Asian Americans.

Because CF is one of the most common genetic disorders, the American College of Obstetricians and Gynecologists (ACOG) recommends that all women be offered genetic testing for some CF mutations as part of routine prenatal planning. If you carry the trait, your partner will be offered screening as well.

Among Caucasians, the chance that both parents are carriers is 1 in 841. If you and your partner are both carriers, the odds are 1 in 4 that your baby will have CF.

No screening test is 100 percent accurate, but if both you and your partner are negative for the CF mutation, your chance of having a baby with the condition is less than half of one percent.

Sickle cell screening

High-risk groups include people of African, Caribbean, South or Central American, Mediterranean, Indian, or Arabian descent. According to the National Institutes of Health, 1 in 13 African Americans carries the gene for this disorder.

If you're a carrier, your partner will be offered testing as well. If you and your partner are both carriers (or your partner is a carrier of a related blood disorder), your baby's chance of having sickle cell disease is 1 in 4.

Thalassemia screening

Thalassemia encompasses a varied group of inherited blood disorders, including some that are relatively mild and others that may cause severe anemia and other serious problems. More than 2 million people in the United States carry the genetic trait for it.

High-risk groups include people of Southeast Asian, Chinese, Indian, African, Middle Eastern, Italian, Greek, and Mediterranean ancestry, as well as anyone with a family history of the disease or a family member who is a known carrier.

People who have the thalassemia trait may have a mild form of anemia. If your initial blood count shows that your red blood cells are small but your iron status is normal, further testing will be done to check for the thalassemia trait.

If you're a carrier, your partner should be offered testing as well. If you're both carriers (or your partner is a carrier for another red blood cell disorder like sickle cell disease), your baby is at high risk for the disease.

Tay-Sachs screening

Tay-Sachs is a fatal disease of the central nervous system. About 1 in 250 people in the United States carries the genetic trait for it.

Among Central or Eastern European (Ashkenazi) Jews, French Canadians, and Cajuns, the carrier rate is about 1 in 27. Among Irish Americans, it's 1 in 50. You're considered high risk if you belong to any of these groups or have a family history of the disease.

(Ashkenazi Jews are also at risk for carrying the genes that cause two other severe nervous system disorders – familial dysautonomia and Canavan disease – and over three dozen other diseases as well.)

If you and your partner both carry the gene for Tay-Sachs, your baby has a 1 in 4 chance of having the disease.

Editor's note: This article was reviewed by Jason Flanagan, a member of the National Society of Genetic Counselors.

This Internet site provides information of a general nature and is designed for educational purposes only. If you have any concerns about your own health or the health of your child, you should always consult with a physician or other healthcare professional. Please review the Terms of Use before using this site. Your use of the site indicates your agreement to be bound by the Terms of Use.

This site is published by BabyCenter, L.L.C., which is responsible for its contents as further described and qualified in the Terms of Use.